Voice communication systems and speech recognition systems typically use acoustic microphones to pickup a user's speech via the sound waves produced by the user talking. The speech is then converted into digital form and used in various types of digital signal processing applications, including voice activity detection for the purposes of noise suppression, speech enhancement, and user interfaces that are based on voice recognition inputs.
An in-the-ear microphone system has been suggested which simultaneously uses both a bone and tissue vibration sensing transducer (to respond to bone-conducted lower speech frequency voice sounds) and a band limited acoustical microphone (to detect the weaker airborne higher speech frequency sounds) within the ear canal. Such a technique allegedly improves speech intelligibility, which is particularly useful for voice recognition systems. The vibration sensing transducer can be an accelerometer, which can be mounted firmly to the inside wall of the housing of an earphone by an appropriate cement or glue, or by a friction fit.